1. Field of the Invention
This invention relates to a radiographic intensifying screen, and more particularly, to a radiographic intensifying screen comprising a support and at least one phosphor layer provided thereonto which comprises a binder and a phosphor dispersed therein.
2. Description of the Prior Art
In radiography used in a variety of fields such as diagnosis and nondestructive inspection, a radiographic intensifying screen is generally employed in close contact with one or both surfaces of a radiographic film for enhancing the speed of a radiographic system. The radiographic intensifying screen comprises a support and a phosphor layer provided thereon. A transparent film is generally provided on the free surface of the phosphor layer to keep the phosphor layer from chemical and physical deterioration.
The phosphor layer comprises a binder and a phosphor dispersed therein. When excited with a radiation such as X-rays supplied through an object, the phosphor emits light of high luminance in proportion to the dose of the radiation. The radiographic film positioned in close contact with the surface of the intensifying screen is exposed to the light emitted by the phosphor, in addition to direct exposure to the radiation supplied through the object. As a result, the radiographic film can be sufficiently sensitized to form a radiation image of the object, even if the radiation is applied to the object at a relatively small dose.
It is required for the radiographic intensifying screen with the aforementioned basic structure to have a high radiographic speed, and to provide an image of high quality (sharpness and graininess). In order to improve the radiographic speed of the intensifying screen and the quality of the image provided thereby, various proposals have been previously made.
For enhancement of the radiographic speed of an intensifying screen, it has been known to provide a light-reflecting layer between the support and the a phosphor layer. For instance, the light-reflecting layer is provided by a method involving vapor deposition of a metal such as aluminum, lamination of a metal foil such as an aluminum foil, or coating of a binder solution containing white powder such as titanium dioxide.
The radiographic intensifying screen also ought to have a sufficient mechanical strength to keep itself from separation of the phosphor layer from the support when mechanical shocks such as bending are given to the intensifying screen in the use. Since the intensifying screen is not substantially deteriorated by exposure to a radiation, the intensifying screen can be repeatedly used for a long period. Threrefore, the intensifying screen is required to be resistant to mechanical shocks given (for example, in the operation of changing a radiographic film) and to be free from separation of the phosphor layer from the support.
However, the provision of a light-reflecting layer for enhancement of the radiographic speed likely brings some disadvantageous features into the radiographic intensifying screen. For instance, a light-reflecting layer formed on a support by the above-mentioned coating procedure possibly has not a suitable surface which is appropriate for providing a phosphor layer thereonto, and the bonding between the coated phosphor layer and the light-reflecting layer is sometimes poor. Accordingly, when a light-reflecting layer is provided on a support, it is necessary to further provide an adhesive layer on the surface of the light-reflecting layer. In such a case, the resultant radiographic intensifying screen shows decrease in the flexibility, as well as in the mechanical strength. Further, where the light-reflecting layer is formed by applying a coating solution containing a binder and a white powder such as titanium dioxide onto the support, the light-reflecting layer has to be formed in a relatively large thickness to achieve the desired high light-reflectivity, and as a result, the flexibility of the resurtant intensifying screen is decreased.